This invention relates to the combustion of organic waste material, and particularly to a closed cycle combustion of waste material using concentrated oxygen.
Waste materials such as municipal solid waste, waste water treatment sludge, and paper mill sludge, are often treated by incineration. Such waste material contains organic combustible matter and inorganic metal oxides. The organic combustible matter typically provides sufficient thermal energy during combustion to maintain high combustion chamber temperatures without the need for supplemental fuel. The inorganic portion of the waste material is characterized by the presence of some silica (SiO.sub.2) and other glass forming metal oxides. If a slagging combustor such as a rotary kiln or cyclone furnace is used for combustion, the inorganic portion of the waste material can reach a temperature high enough to melt. The resulting molten material is drained from the combustion chamber as slag.
Conventional incinerators designed to combust organic waste material use air as the oxidizer source. Since almost four-fifths of air is inert gases (primarily nitrogen), a major portion of the air provides no benefits to the combustion process. In fact, the inert gas causes several distinct disadvantages. A first disadvantage is that the combustion flame temperature is lowered, thereby making it difficult to maintain the necessary temperatures to melt the inorganic metal oxides in the waste material. Secondly, the waste gases from the incineration will be contaminated with substantial amounts of nitrogen that results in a large volume of exhaust gases which require further treatment before release into the atmosphere.
It has been proposed to reduce the undesirable effects of nitrogen in the incineration of hazardous waste by introducing concentrated oxygen into the combustion chamber along with recycled exhaust gases. See U.S. Pat. No. 5,309,850 issued May 10, 1994, to Downs, et al.
The present invention also uses concentrated oxygen in a closed cycle to treat non-hazardous waste and to convert the waste material into useful end products.